The present invention relates to communications systems and, more particularly, to a method for adaptive control of access to a wireless telecommunication system.
In cellular communication systems, such as a code division multiple access (CDMA) communication system, a subscriber unit or mobile station and a fixed network unit or base station establish a two-way communication link through forward and reverse radio frequency (RF) communication links. The forward communication links originate from the base station and the reverse communication links from the mobile station. The base station normally communicates simultaneously to a number of mobile stations. An example of such a system is described in the Telecommunications Industry Association/Electronic Industry Association Standard 95B (TIA/EIA/IS-95-B).
When too many subscribers access a system at the same time, the system enters a degraded state. The degradation affects both the subscriber and the system. System degradation is due to collisions on the control channel. FIG. 1 is a plot of access channel throughput versus offered traffic measured through the number of access attempts per slot time for an exemplary cellular telecommunication system. As shown in FIG. 1, the system throughput steadily increases up to an ideal point at an offered traffic rate of 1.0. Beyond this point, system degradation is evident.
In conventional systems, the media access controller or base station controller broadcasts an access restriction value to the subscriber units on a paging channel in an attempt to keep the system operating on the left side of the throughput curve. The access restriction value is used by each subscriber unit to calculate when to initiate another access attempt. Unfortunately, in conventional systems, the media access controller cannot determine on which side of the throughput curve the subscriber unit is functioning. This is partially due to the fact that in conventional cellular telecommunication systems, it is impossible to determine how many attempts a subscriber made before successfully initiating an access. Therefore, the media access controller indiscriminately broadcasts access restriction values based on a static database configuration in order to cut off excess traffic.
Accordingly, it has been considered desirable to develop a new and improved method and apparatus for adaptively controlling access to a shared media that meets the above-stated needs and overcomes the foregoing difficulties and others, while providing better and more advantageous results.
For instance, one advantage of the present invention is that it provides a more robust system with better throughput.
Another advantage of the present invention is the provision of a cellular communications system which accommodates geographic loading differences.
Yet another advantage of the present invention is that more call attempts will succeed when the system is experiencing a heavy load.
Still another advantage of the present invention is the provision of a dynamic assignment of access restriction values based on actual load instead of a static database configuration.
A further advantage of the present invention is that it selectively reduces less important traffic components, better accommodating all classes of subscriber during emergency situations.
Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.